FIG. 1 illustrates a typical knee joint including a femur 1 and a tibia 3, shown with healthy femur cartilage 5 and healthy tibia cartilage 7. The knee joint includes three primary elements: a medial tibiofemoral joint, a lateral tibiofemoral joint, and a central patellofemoral joint. Joint trauma or diseases such as osteoarthritis and rheumatoid arthritis can cause severe damage to one or more of these elements. In a case where one or more of the knee elements are traumatized or diseased, while the other one or two knee elements are healthy, the traumatized or diseased element(s) can be replaced in a partial knee replacement surgical procedure. In a case where all three primary elements are traumatized or diseased, all three elements can be replaced in a total knee replacement surgical procedure.
In both partial and total knee replacement surgical procedures, the traumatized or diseased ones of the knee's bony surfaces, e.g., femur, tibia, and patella, can be replaced by prosthetic components. The knee's soft-tissue structures, particularly ligaments surrounding the knee joint, can be largely left intact. The knee's major ligament structures include medial and lateral collateral structures, and anterior and posterior cruciate ligaments. These ligamentous structures play a significant role in controlling the motion and stability of a knee joint. With regards to the cruciate ligaments, the posterior cruciate ligament (PCL) is generally present and well-functioning in patients undergoing partial or total knee replacement surgery. However, in at least some patients, the anterior cruciate ligament (ACL) can be absent or non-functional at surgery due to prior trauma or gradual degradation.
Traditional partial knee replacement prostheses have no mechanism for substitution of ACL function. Consequently, patients with an absent or non-functional ACL may end up receiving total joint replacement, which is a generally more invasive procedure than partial knee replacement and which replaces the healthy element(s) of the patient's knee. Alternatively, instead of total knee replacement, patients with an absent or non-functional ACL may undergo additional surgery prior to a partial knee replacement surgical procedure to reconstruct the ACL, such as with a soft tissue graft.
In traditional total knee replacement surgical procedures, patients receive a type of prosthesis, e.g., a cruciate retaining (CR) type implant, that allows the present and well-functioning PCL to be retained. However, even for patients who have a functional ACL, the ACL is traditionally resected during surgery prior to implantation of a CR type implant because of difficulty in achieving optimal soft-tissue balancing and component placement with both the ACL and PCL present. However, traditional CR prostheses have no mechanism for substitution of the ACL function. Consequently, following CR prosthesis implantation, the knee shows abnormal motion patterns characterized by features such as reduced tibial internal rotation and paradoxical anterior femoral translation.
Accordingly, there remains a need for improved knee prostheses and methods for treating disease and trauma affecting the knee.